Processors, memory devices, imagers and other types of microelectronic devices are often manufactured on semiconductor workpieces or other types of workpieces. In a typical application, several individual dies (e.g., devices) are fabricated on a single workpiece using sophisticated and expensive equipment and processes. Individual dies generally include an integrated circuit and a plurality of bond-pads coupled to the integrated circuit. The bond-pads provide external electrical contacts on the die through which supply voltage, signals, etc., are transmitted to and from the integrated circuit. The bond-pads are usually very small, and they are arranged in an array having a fine pitch between bond-pads. The dies can also be quite delicate. As a result, after fabrication, the dies are packaged to protect the dies and to connect the bond-pads to another array of larger terminals that is easier to connect to a printed circuit board. The dies can be packaged after cutting the workpiece to separate the dies (die-level packaging), or the dies can be packaged before cutting the workpiece (wafer-level packaging).
Conventional die-level packaged microelectronic devices include a microelectronic die, an interposer substrate or lead frame attached to the die, and a molded casing around the die. The bond-pads of the die are typically coupled to terminals on the interposer substrate or the lead frame. In addition to the terminals, the interposer substrate also includes ball-pads coupled to the terminals by conductive traces supported in a dielectric material. Solder balls can be attached to the ball-pads in one-to-one correspondence to form a “ball-grid array.” Packaged microelectronic devices with ball-grid arrays are generally higher-grade packages having lower profiles and higher pin counts than conventional packages using lead frames.
Packaged microelectronic devices such as those described above are used in cellphones, pagers, personal digital assistants, computers, and many other electronic products. To meet the demand for smaller electronic products, there is a continuing drive to increase the performance of packaged microelectronic devices, while at the same time reducing the height and the surface area or “footprint” of such devices on printed circuit boards. Reducing the size of high performance devices, however, is difficult because the sophisticated integrated circuitry requires more bond-pads, which results in larger ball-grid arrays and thus larger footprints. One technique for increasing the component density of microelectronic devices within a given footprint is to stack one device on top of another.
One concern with many high-density packaged microelectronic devices is electromagnetic emissions or radiation generated by the devices during operation. Such electromagnetic disturbances are often referred to as electromagnetic interference (“EMI”). EMI within a particular system or device generally occurs as a result of the generation and/or transmission of electromagnetic radiation by integrated circuits, power supplies, or other radiation sources. Left unchecked, EMI can produce a number of undesirable effects. For example, EMI can interfere with or impair the operation and integrity of unshielded equipment and/or systems proximate to the source of the emissions. Furthermore, EMI can significantly degrade or otherwise negatively affect the performance of unshielded devices.
One approach to addressing the problems with EMI is to shield or ground the integrated circuitry within packaged microelectronic devices. A conventional method for shielding lead frame devices, for example, includes forming a conductive backplane on a back side of the wafer. Portions of the lead frame can then be electrically coupled to the backplane, and one or more bond-pads can be electrically coupled to the backplane via the corresponding portions of the lead frame to ground the device. One significant drawback with this approach, however, is that it is not suitable for devices with small arrays of back side contacts (e.g., ball-grid arrays) because (a) many of the ball-pads or back side contacts should not be grounded or otherwise connected in common, and (b) the remaining ball-pads or back side contacts cannot be connected to the backplane using wire-bonding or other conventional techniques. Accordingly, there is a need to provide the methods for packaging microelectronic devices having small arrays of back side contacts and conductive backplanes.